Railway track consists of two parallel rails, extended in length for seemingly endless runs. The rails are actually formed from comparatively short rail sections, each of thirty nine or eighty feet length (as fabricated by the rail manufacturer) that are laid end-to-end, with the adjacent ends then either being welded or mechanically connected together. The welded joints, between the shorter (39 or 80 foot) rails may be made up in a rail welding plant, to define continuously welded rail sections, each about one-quarter mile in length, that are then carried on a special rail train to the use site, and dropped off end-to-end as needed; or may be made in the field.
Of importance, the two rails of the track must be exactly spaced apart, to the proper guage; the top running surfaces of adjacent rails, across each separate connection, must be accurately aligned; and if mechanically connected together, the rail ends may only be separated across a small gap.
Mechanical connections between the rail ends use special bars, located opposite one another or both the inside (guage side) and outside (field side) of the rails, each overlapping a short length of each rail; and fastening means that extend through aligned holes in the rails and bar operable to clamp the bars tightly against the rails.
The joint bar may have enlarged top and bottom portions connected together by a narrower web; and contact faces intended to cooperate with specific head and base regions of the rails may be formed on these enlarged top and bottom portions. These contact faces would be specifically shaped and orientated to be flush against the intended head and base regions of the rail.
The rails used by railroads throughout the country are different in size, weight, and/or cross section. By way of example, track on main lines are typically made up of heavier rail stock, weighing in the range of 115-152 pounds per three feet (yard) rail length; while track on some secondary lines may use lighter rail stock, in the range of 70-112 pounds per three foot (yard) rail length. These dissimilar rails vary somewhat with respect to any of many dimensions, including the overall size and shape, and the relative location of the rail head and rail base. Consequently, each specific size of rail would need one specific size of connection bar, with its specific contact faces.
For connecting identical rails together, the contact faces on the different ends of the bar are similar to, and axially aligned with, one another; although different bars may be needed for the field and guage sides of each rail, as right-hand and left-hand images. Such bars are simply referred to as "joint bars"; each being sized for a specific rail section, having a specific cross section, length and hole spacing (such as 24 inches for a four holes, 30 inches for five holes, or 36 inches for six holes), to match a particular rail having a particular rail end drilling.
A conventional joint bar is formed by a specialist, by hot rolling steel bar stock to shape, to provide the intended contact faces; and is then cut to length, and hot punched to provide the holes for the fastening means. Such joint bars are fabricated of standard stock steel, having medimum carbon content, such as AISI C1020 or C1030; and are not made of high carbon steels.
For connecting dissimilar rails, the different size or weight, bars more complicated in shape and configuration are needed . . . known as compromise bars. The typical compromise bar may have the contact faces, defined at the opposite ends of the bar, of different configurations and/or axial alignments (offset vertically and/or horizontally). These differences may be slight (measured in thousandths of an inch) and/or significant (measured in tenths or an inch).
A conventional compromise bar is formed from a conventional joint bar sized for the larger of the two rails, with the opposite end and/or both ends then being mechanically reformed to approach the specific spacing and configuration needed for defining both ends of the bar. To do this, joint bar stock, initially at the approximate length of the intended compromise bar, is heated, and is then mechanically pressed between crude dies in a large hydraulic press. The exact intended compromise bar configuration is rarely achieved solely by the compression dies, so that the bar must then be trimmed and machined, to even approach tolerance. The compromise bar must also be heat treated, quenched, and scaled; and thereafter, may even have to be further trimmed and machined.
Conventional compromise bars reformed in this manner appear to have several major drawbacks, being: poor tolerances of, and structural weaknesses that crop up in, such bars; resulting in undue risk of and/or actual failures of such bars.
Thus, compromise bars intended to interconnect two rails of significantly different size or shape, must have one bar end reformed into a much smaller overall configuration, requiring significant repositioning and/or removal of the conventional joint bar material. After such reforming, it is not uncommon to have the bar web at the smaller bar end bowed significantly; and even though attempts may be made to straighten a bowed web in a different hydraulic press, complete straightening seldom can be achieved, while retaining the desired overall shape or size of the compromise bar. Machining the excess material off may produce a condition, that the contact faces are on structure below design thickness. On the other hand, conventional compromise bars intended to interconnect two rails of roughly the same size, may not be accurately reformed by the mechanical compression dies, since the dies are typically too crude and/or too insensitive to establish small differences between the offsets or alignments of, or the contact face configurations at, the opposite bar ends; again requiring machining to approach the desired tolerances.
A compromise bar outside of tolerance, may generate stress concentrations in the components; and/or may cause the rail surfaces at the rail ends to be misaligned, creating an excessive interruption across the rail joint. Such conditions could be dangerous until repaired and could lead to field failure . . . and expensive repair.
The mechanical reforming steps needed to reshape the conventional joint bar to approach the shape of the intended compromise bar, set up residual internal stresses in the reformed compromise bar; even though the bar is hot during the reforming steps, and even though the reformed bar may be subsequently quenched. It has been speculated that the greatest stresses may be generated in the regions that are most reformed; and one such regional typically is between the opposite ends of the bar, adapted to bridge the gap between the rail ends. The joint bar stock reformed to the compromise bar, is available only in medium carbon steels. In order to provide adequate hardness to comply with railroad standards, rapid quenching may be required, and such may make the bar brittle and susceptible to surface stress cracking. These structural drawbacks and stress concentrations may be particularly critical in many geographical locations of possible use in this country, where the joint bar will be exposed to very low temperatures, many degrees below freezing.
Commonly, the conventional joint bars and the conventional compromise bars fail in the region between the two bolt holes that correspond to the first hole spaced in from each rail end; frequently through the bolt hole itself, and frequently where the bar actually bridges the gap between the rail ends.